A mass spectrometry system is an analytical system used for quantitative and qualitative determination of the compounds of materials such as chemical mixtures and biological samples. In general, a mass spectrometry system uses an ion source to produce electrically charged particles such as molecular and/or atomic ions from the material to be analyzed. Once produced, the electrically charged particles are introduced to the mass spectrometer and separated by a mass analyzer based on their respective mass-to-charge ratios. The abundance of the separated electrically charged particles is then detected and a mass spectrum of the material is produced. The mass spectrum is analogous to a fingerprint of the sample material being analyzed. The mass spectrum provides information about the mass-to-charge ratio of a particular compound in a mixture sample and, in some cases, molecular structure of that component in the mixture.
The molecular weight of a compound is often determined by the use of a mass spectrometry system having a single mass analyzer. The mass analyzer may include a quadrupole (Q) mass analyzer, a time-of-flight mass analyzer (TOF-MS), an ion trap mass analyzer (IT-MS), etc. Tandem mass spectrometers (i.e., tandem-MS or MS/MS) are often needed to analyze samples having complicated molecules. Tandem mass analyzers typically include two mass analyzers of the same or different type (e.g., TOF-TOF MS and Q-TOF MS).
In a tandem mass spectrometric analysis, electrically charged particles are transmitted to the first mass analyzer and an ion of particular interest is selected. The selected ion is transmitted to a dissociation cell where the selected ion is fragmented. The ionic fragments of the dissociated ion are transmitted to the second mass analyzer for mass analysis. The fragmentation pattern obtained from the second mass analyzer is then analyzed to determine the structure of the corresponding molecule.
There are challenges in building a high performance mass spectrometer such as a mass spectrometer having high sensitivity, high resolution, high mass accuracy, and wide dynamic range. One challenge is how to efficiently use sample material, which includes maximizing ionization efficiency and then efficiently transmitting formed ions into a mass analyzer.
However, for many mass spectrometric applications, high loss occurs when transmitting ions from a high-pressure region where ions are usually generated, to a low pressure region in the mass analyzer. This ion loss is a result of relatively long distances needed for differential pumping stages and of ion-molecule collision with a background gas when ions travel this distance. This is especially found in situations where ions are generated at atmospheric pressure or relatively high gas pressure. Such applications include, for example, electrospray ionization mass spectrometer (ESI-MS), atmospheric pressure chemical ionization mass spectrometer (APCI-MS), atmospheric pressure matrix assistant laser desorption/ionization (AP-MALDI), inductively coupled plasma mass spectrometry (ICP-MS) and glow discharge mass spectrometry (GDMS).
Ion optic devices have been used for transmitting charged particles and manipulating a beam of charged particles. In particular, ion optic devices have been used, for example, for focusing or defocusing of a beam of charged particles and for changing the particle energy and the energy distribution of the beam. Prior approaches to the above devices generally can be divided into two categories. Some known devices use magnetic fields or electrostatic fields in various configurations. Such devices include, for example, electrostatic einzel lenses, multipole lenses and electrostatic or magnetic sector fields. Other known devices use a radio frequency (RF) electrical field such as that employed in RF multipole ion guides and RF ion funnels, which consist of a series of ring electrodes. In comparison to those approaches that employ an electrostatic field, ion optic devices using a RF field offer significantly higher transmission efficiency and the ability to modify ion energy by collisional cooling when utilized with a gas of intermediate pressure. Another advantage is the use of the RF field for collisional induced dissociation (CID) to produce fragment species from molecular ions, which is an important tool for study of molecular structure. In commercial mass spectrometric instruments, RF multipole ion guides are widely used.
In collision induced dissociation, a multipole ion guide also acts as a collision cell. When molecular or polyatomic ions collide with the background gas (normally an inert gas), a portion of the translation energy of the ions converts into activation energy that is sufficiently high enough and certain molecular bonds are broken. The fragment pattern produced characterizes the original molecule and provides information about its structure. In such applications, a multipole ion guide is placed between two mass spectrometers to form a tandem MS and is used to confine both the parent ions and the fragments of the parent ions otherwise referred to as daughter ions. Confinement of the ions is generally realized by use of an oscillating electrical potential field.
A conventional electric RF multipole ion guide may be constructed by using several (even numbers) circular electrically conductive rods of identical geometric dimension arranged parallel around the central axis of the multipole ion guide. When radio frequency voltages of opposite polarities, U+V cos(xcfx89t) and xe2x88x92[U+V cos(xcfx89t)] are alternately applied to the adjacent rods, a symmetric RF field is established inside the radius of the multipole ion guide. In accordance with the numbers of rods, such fields are classified as quadrupole, hexapole and octopole, and so forth, for four rods, six rods and eight rods, respectively. At any cross section of the RF multipole field, the potential distribution is a function of time and is characterized by the RF frequency (xcfx89).
An ion beam sent axially trough the multipole field experiences a transverse force, which varies in time and space. It can be shown that the motion of the ions in such a field is harmonic. Due to such oscillation, ions are forced to xe2x80x9cstayxe2x80x9d inside of the inner circus of the multipole structure while traveling through the multipole structure. Consequently, the ion beam can be transmitted over a long distance without significant loss, which is essential for achieving high instrument sensitivity.
However, there is a need in the industry for a high performance device, which efficiently facilitates ion transmission, cooling, and/or focusing. In addition, there is a need for a device which offers high fragmentation efficiency for large organic or biomolecules. These and/or other shortcomings are addressed herein
Ion guides and systems and methods for involving the use of ion guides are disclosed. Briefly described, one exemplary system, among others, includes an ion guide. The ion guide includes a first structure and a second structure. The second structure is coaxially disposed within the first structure. The second structure includes at least three groups of openings through a wall of the second structure that are distributed around a circumference of the second structure. In addition, at least one of the groups of openings is offset from the other groups of openings by a multiple of a constant rotation angle around the circumference of the second structure.
An exemplary method of focusing, among others, can be broadly summarized by the following steps: forming an oscillating electric potential field having predetermined characteristics, forming a rotating electric potential field superimposed on the oscillating electric potential field having predetermined characteristics, and introducing, the ions to the oscillating electric potential field and the rotating electric potential field.
Other systems, methods, features and/or advantages of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods features, and/or advantages be included within this description and be protected by the accompanying claims.